Field of the Disclosure
The present disclosure relates generally to a media path assembly in an imaging device, and, more particularly, to a system and method for controlling media bubble formation in the imaging device.
Description of the Related Art
Imaging devices, such as an electrophotographic printer, typically monitor and control the movement of media sheets at various points along the media path to ensure adequate print quality. Example areas where media sheet movement is carefully monitored and controlled are the toner transfer nip and the fusing nip. The toner transfer nip and fusing nip each function to move the media sheet along a media path section in addition to their respective toner transfer and fusing functions. If the media sheet moves too quickly or slowly through the toner transfer nip, toner images may not be adequately transferred to the media sheet which may result in print defects. The speed of the media sheet through the fusing nip may also be controlled to optimally fix toner to the media sheet.
The media sheet may move at different speeds along different sections of the media path. For example, the media sheet may move at a different speed through the fuser nip than it moves through the toner transfer nip. In some existing imaging devices, the distance between the toner transfer nip and fusing nip is less than the length of a typical media sheet such that the media sheet may be present in both the transfer nip and the fuser nip at the same time. In this case, if the fuser nip is driven faster than the toner transfer nip, the fuser nip may drag the media sheet and cause print defects. On the other hand, if the fuser nip is driven slower than the toner transfer nip, a bubble will form in the media sheet. The size of the bubble generally depends on the relative speeds between the two nips. If the bubble size is too large, the media sheet may contact elements outside of the media path, which may disturb the toner image on the media sheet, deposit unwanted toner on the media sheet, or otherwise adversely affect print quality. On the other hand, having a bubble size that is too shallow introduces the risk of dragging the media sheet caused by variation in the speed through the fusing nip. Thus, controlling the bubble size is important to maintain image quality. Prior art imaging devices incorporate a bubble sensor between the toner transfer nip and fusing nip in order to sense and control bubble growth on media sheets being fed between the two nips.
In an imaging device employing a reference-edge media feed system in which a side edge of a media sheet rides along a reference edge of the imaging device during feeding, the bubble sensor is typically positioned near the reference edge to allow bubble detection on a wide range of media sizes, including the narrowest media supported. During feeding, the bubble sensor touches the media sheet and applies a drag force on the media sheet. When narrow media is fed, the drag force applied on the media sheet is relatively close to its centerline allowing the media sheet to be fed into the fusing nip without skew or an objectionable amount thereof. However, when wider media is fed, feed reliability may be comprised. This is because the drag force applied by the bubble sensor is positioned farther from the centerline of the wide media which creates a moment on the media sheet that skews the media sheet which may result in poor entry into the fusing nip. Poor entry into the fusing nip may cause print defects. It would be advantageous to be able to reduce, if not eliminate, the imbalance applied on wide media sheets during feeding while maintaining the control of bubble formation.